On Sat, May 30, 2009 at 5:48 PM, Bertram Felgenhauer
Sterling Clover wrote:
This is perhaps a silly idea, but perhaps useful -- there should be a version of unsafePerformIO that always does the "right" thing with regards to exceptions. From that, the other unamb primitives can perhaps be built more obviously? Additionally, this implementation would be potentially useful to libraries beyond unamb.
You mean something like this?
-- | A version of 'unsafePerformIO' that assures that the resulting -- (pure) computation can be restarted if it is killed by an -- asynchronous exception. Note that as a result, the IO action -- may be performed more than once. exceptionSafeUnsafePerformIO act = unsafePerformIO $ retry act where retry act = unblock act `catch` \SomeException e -> do myid <- myThreadId throwTo myid e retry act
That could be useful indeed.
Let's call it restartingUnsafePerformIO, though. It's not in any way "safer" than the normal one - in a number of circumstances it's less safe. Besides that, I've turned in a patch documenting this discussion in Unamb.hs. You can see the resulting commentary in http://brage.info/~svein/unamb.patch for the time being; feel free to tell me it's mistaken in some respect. -- Svein Ove Aas